Interface selection in a moving network

ABSTRACT

A method of establishing a traffic route for a mobile network node attached to a mobile router, where the mobile router has a plurality of upstream interfaces available to it. The method comprises sending from the mobile router to the mobile node, identifiers of the interfaces and of their properties, the identifiers mapping to IPv6 traffic classes or IPv4 type of service. In the case of IPv6, the identifiers may be contained within router advertisement messages broadcast by the mobile router. At the mobile network node, an interface is chosen based upon the identified interface properties. The traffic class or type of service field of at least certain outgoing packets includes the identifier of the chosen interface. At the mobile router, packets are routed across the interface corresponding to the identifier contained in the traffic class or type of service fields, typically using rules created upon detection of a traffic class value in a packet header.

TECHNICAL FIELD

The present invention relates to interface selection in a moving networkand in particular to the selection of an interface upstream of a mobilerouter by a mobile network node located downstream of that mobilerouter.

BACKGROUND

Trains, busses, airplanes and Personal Area Networks (PANs) are examplesof use cases where moving network technologies can be applied. A movingwireless network is a cluster consisting of Mobile Network Nodes (MNNs)and Mobile Routers (MRs). A Mobile Router routes IP traffic between aMNN and the Internet (or other IP network). The Mobile Router acts as anaccess point for the MNN. A Mobile Router may be connected to anothermoving network or directly to the Internet via an access point (AP). Inthe former case, a set of nested mobile networks results. The IETF RFC3963 proposes a Network Mobility (NEMO) protocol according to thisarchitecture.

According to IETF RFC 2461, a Mobile Router broadcasts RoutingAdvertisement (RA) messages to advertise its existence and to informMNNs that it provides a mobile routing service. The RAs may contain anoperator identifier, for example, to aid selection of an appropriatenetwork by a user. When a MNN finds a suitable Mobile Router, the MNNtriggers an attachment exchange with the Mobile Router.

It will be appreciated that when a Mobile Router changes its point ofattachment to the Internet, or is handed-off to another Mobile Router,the locations (i.e. IP addresses) of all of the downstream MNNs willchange. In order to maintain service continuity during and afterhand-off of a Mobile Router, some mechanism is required in order toensure that data sent from peer (or correspondent) nodes involved in acommunication session with the MNN is sent to the MNN at the node's newlocation. The approach adopted by NEMO involves the creation of a tunnelbetween the Mobile Router and some home router (or “home agent”) withinthe fixed network. All traffic sent from a Peer Node to a MNN (andpossibly traffic sent in the reverse direction) is routed through thetunnel. When the Mobile Router changes its location, it sends an updateto the home router. It may be possible for the MNN to delegateresponsibility for location update signalling to an upstream MobileRouter. The key point however is that the network prefix used by the MNNremains unchanged as the Mobile Router moves.

A Mobile Router performs home registration of its upstream or “egress”interface as described in the MIPv6 specification to allow for changesin the point of attachment of the interface to the Internet. When theMobile Router uses multiple egress interfaces it can have more than onehome registration at the same time. This is described in the IETFmonami6 working group specification related to multiplecare-of-addresses (MCoA).

As well as having multiple egress interfaces, a MR may provide multipledownstream or ingress interfaces. The MR must allocate a differentnetwork prefix to each of the various ingress interfaces. These multiplenetwork prefixes must be registered with the HA in addition to thenormal MIPv6 home registration. MNNs or “hosts” attached to the ingressinterface of the Mobile Router configure IPv6 addresses using the prefixappropriate for the chosen interface, and the Mobile Router tunnels alltraffic from the MNNs attached to the ingress interface to the HomeAgent (HA) of the Mobile Router. The HA then sends this traffic to theInternet. All traffic which is addressed to a network prefix delegatedto an ingress interface of the Mobile Router arrives at the HA, whichintercepts the traffic and forwards it to the Mobile Router which inturn routes it to the correct ingress interface.

When a Mobile Router has more than one home registration (i.e. it hasmultiple egress interfaces) it also has more than one route between theHA and itself. The traffic characteristics of these different pathsbetween the HA and Mobile Router can be quite different. However, MNNsattached to the ingress interface(s) of the Mobile Router do not knowanything about the egress interfaces of the Mobile Router and what kindof services the Mobile Router can offer through these. In addition, evenif a MNN attached to an ingress interface of the Mobile Router couldinfluence the choice of egress interface through which outgoing packetsare routed, it is not easy to see how the MNN could influence thedownlink path that packets take from the HA to the Mobile Router.

SUMMARY

The present invention provides a method for a Mobile Router withmultiple egress interfaces to inform downstream Mobile Network Nodes ofthe Mobile Router's upstream interfaces and their characteristics. Inthe case of IPv6, notification may be achieved using a new RouterAdvertisement (RA) option which includes an identifier and acharacteristics descriptor. When a Mobile Network Node receives such anRA option, it learns the capabilities of its next-hop router, that isthe Mobile Router, and may set the Traffic Class field in the IPv6header accordingly. The identifier may have the format of an 8-bitinteger which can be directly mapped to the Traffic Class (TC) fieldfound in the IPv6 header. This allows the Mobile Router to routeoutgoing packets using the desired interface. In the case of IPv4, thetype of service (ToS) field may be employed instead of the Traffic Classfield.

The terms Traffic Class and Type of Service have specific meanings interms of the existing IPv4 and IPv6 standards. However, it will beappreciated that in future standards, different terms may be employed,and it is intended that these also will fall within the scope of thisinvention. In particular, it is intended that the invention applies toall cases where the interface identifiers are mapped to fields theintended purpose of which is to identify and distinguish betweendifferent classes or priorities of packets.

According to a first aspect of the present invention there is provided amethod of establishing a traffic route for a mobile network nodeattached to a mobile router, where the mobile router has a plurality ofupstream interfaces available to it. The method comprises sending fromthe mobile router to the mobile node, identifiers of the interfaces andof their properties, the identifiers mapping to IPv6 traffic classes orIPv4 type of service. In the case of IPv6, the identifiers may becontained within router advertisement messages broadcast by the mobilerouter. At the mobile network node, an interface is chosen based uponthe identified interface properties. The traffic class or type ofservice field of at least certain outgoing packets includes theidentifier of the chosen interface. At the mobile router, packets arerouted across the interface corresponding to the identifier contained inthe traffic class or type of service fields, typically using rulescreated upon detection of a traffic class value in a packet header.

The invention makes it possible for a Mobile Network Node to selectwhich outgoing interface should be used on the Mobile Router. Withoutthis kind of mechanism the data might be sent out on an interface whichis not preferred (in terms of bit-rate, cost, etc) for this traffic.

According to a second aspect of the present invention there is provideda mobile router comprising means for providing a plurality of upstreaminterfaces. These could, for example, be a WLAN interface and a 3Ginterface. A first transmitter is provided for sending to a mobilenetwork node identifiers of the interfaces and of their properties, theidentifiers mapping to IPv6 traffic classes or IPv4 type of service. Areceiver receives packets from downstream mobile network nodes. Therouter comprises means for mapping traffic class or type of servicefields within at least certain received packets to upstream interfaces,and a second transmitter for causing packets to be routed across theinterfaces corresponding to the identifiers contained in traffic classor type of service fields.

According to a third aspect of the present invention there is provided amobile network node comprising a receiver for receiving from a mobilerouter identifiers of the upstream interfaces available to the mobilerouter and of their properties, the identifiers mapping to IPv6 trafficclasses or IPv4 type of service, means for choosing an interface basedupon the identified interface properties, and means for including in thetraffic class or type of service field of at least certain outgoingpackets, the identifier of the chosen interface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically a moving wireless network comprising aMobile Network Node attached to a Mobile Router;

FIG. 2 illustrates schematically the structure of a new options field ofa Router Advertisement message for accommodating an interface identifierand associated properties; and

FIG. 3 is a flow diagram illustrating the overall operation of a routeselection mechanism.

DETAILED DESCRIPTION

FIG. 1 illustrates a moving network 1 which comprises a Mobile Router(MR) 2 and one or more Moving Network Nodes (MNNs) which are attached tothe MR. The Figure illustrates only a single MNN 3. The MR 2 is assumedto have available to it two upstream or egress interfaces associatedrespectively with wireless access networks AN1 and AN2 (identifiedrespectively by reference numerals 4 and 5). AN1 and AN2 allow the MR toconnect to the Internet 7 (or other IP network). In a typical scenario,AN1 and AN2 could be respective WiFi networks, or could be Wi-Max,cellular telephone networks, etc. In some cases, the access networks maycorrespond to different access technologies within the same accessnetwork, or indeed may use the same access technology within the sameaccess network but correspond to different link qualities.

The MR 2 is required to register a care-of-address (CoA) for each of itsegress interfaces with a Home Agent (HA) 6 using the MCoA extension toMIPv6. The HA is located within a home network of the MR, typicallywithin a cell phone network operator's core network and to which theoperator of the MR is a subscriber. As is well known, the HA acts as ananchor point for data flowing between the MR and correspondent nodes. Aswell as registering a CoA for each egress interface, the MR learns thecapabilities of its access networks and adds this information to theRouting Advertisement (RA) messages that it broadcasts periodically. AMNN receiving a RA message can then use this information to let the MRknow which egress interface is preferred for the outgoing traffic. TheMR can set or change rules within the HA associated with the interfaces.The use of rules within the HA is described further below. [Thisarchitecture does not preclude the MNN itself employing a mobilityprotocol, adding a further HA to the traffic path.]

IPv6 specifies (RFC 2461 chapter 4.2) that RA messages may contain“options” fields. In this case, the MR adds one RA option for eachegress interface containing an identifier for the interface anddescribing the characteristics of that interface. The structure of thenew RA option is illustrated in FIG. 2. The Type and Length fields areas described in the relevant RFC. The ID field defines the identifierwhich the MNN must use when it wants to use the access network which hasthe characteristics defined in the Access Network Characteristics field.The length of the Access Network Characteristics field can be determinedfrom the Length field. The Access Network Characteristics field carriesinformation which the MNN uses to determine which egress interface touse for outgoing traffic. The format of this field can be set asrequired.

When applied to IPv6, the ID field is directly mapped to the IPv6header's Traffic Class field as defined in IETF RFC 2460. This allowsthe MNN to tag outgoing packets which should be routed using a specificegress interface on the MR by modifying only the IPv6 header. The resultis that no other signalling is required between the MNN and MR. If theTraffic Class field is already used by some upper-layer protocol, theMNN tunnels the packet to the MR, e.g. using link-local addresses. Inthis case the ID field is included in the Traffic Class field of theouter IPv6 header.

The MR examines incoming packets to determine if a rule has beenestablished mapping the source and destination addresses to an upstreaminterface. If no rule has been established, and if a packet contains avalue in the Traffic Class field, the MR creates a new rule mapping thesource and destination addresses to the interface corresponding to theTraffic Class value. For subsequent outgoing packets belonging to thesame stream, the MR does not have to look at the Traffic Class field: itmerely has to match the source and destination IP addresses to thepre-established rule and select the interface accordingly.

It is possible that the rule established at the MR is maintainedaccording to a fixed length timer. The timer is reset each time a packetis received for a given stream. If the timer expires, the associatedrule is deleted. If the MNN subsequently sends a further packet for thesame stream, the MR must recreate a rule based upon the Traffic Classvalue. By including the Traffic Class value in all packets, the MR canalso detect when a MNN wishes to change the upstream interface for agiven stream. This also facilitates mobility, allowing the MNN to moveto a new MR whilst allowing the new MR to establish an appropriate rule.

Incoming traffic for a MNN attached to the ingress interface of the MRwill arrive at the home link of the MR (identified by the network prefixused by the MNN) and is intercepted by the HA of the MR. If the MR hasregistered more than one CoA, the HA has more than one possible route tochoose from when forwarding this traffic to the MR. However, it willgenerally be preferable to forward this traffic via the same route aswas taken by the outgoing traffic so that the “service” seen by the MNNis the same in both directions. To determine which route to use, the HAconsults its rules (routing table entry, rules, flow binding etc.) whichdefine the traffic path from the HA to the MR for specific trafficflows.

One of the paths between the HA and the MR is specified as a defaultpath. If outgoing traffic from the MNN is using the default path, the MRdoes not have to add a specific rule at the HA for this traffic andrather a default rule is applied. [In this case, a “rule” defines howpackets meeting certain criteria or none should be routed.] However, ifthe MNN has requested that a path other than the default path should beused for its traffic, the MR must add a new rule to the HA to routeincoming traffic (destined for the MNN) via this path. Thus, at the sametime as the MR creates a rule for outgoing packets, it installs acorresponding rule into the HA for routing incoming packets.

The new rule must be negotiated between the HA and the MR. The MR sendsthe new rule to the HA and the HA adds this rule to its rule database.The HA acknowledges receipt of the rule and indicates its acceptance orrefusal. Before a new rule is added the HA will have maintained arouting entry which dictates that all traffic arriving to the delegatedprefix should be sent to the MR via the default path. When the MRinjects a new rule for the MNN, the MR router specifies a collection ofinformation combined both from the IP header (source and destinationaddresses, etc.) and upper layer headers (TCP/UDP ports etc.) touniquely identify the flow to the HA. When the information in anincoming packet matches this information, the HA must forward thistraffic to the MR via the specified route. It is noted that theidentifier which defines the chosen interface need not be communicatedby the MR to the HA. This identifier is merely used between the MNN andthe MR.

FIG. 3 is a flow diagram outlining the processes employed at the MR andthe MNN in order to implement the embodiment described.

Despite determining from the Traffic Class field that the MNN isrequesting that a non-default route be used, the MR can of course choosenot to set the new rule for the MNN, in which case the incoming andoutgoing traffic for the MNN will be routed via different paths.Furthermore, if no mechanism exists for setting rules between the MR andthe HA, this again will result in incoming traffic always being routedvia the default path.

It will be appreciated by the person of skill in the art that variousmodifications may be made to the above described embodiments withoutdeparting from the scope of the present invention. In particular, theinvention may be applied to IPv4, with the interface identifiers beingmapped to ToS values, and the chosen identifier being included in theToS field of outgoing packets. The detailed embodiment described abovemay be modified as appropriate for use with mobility protocols such asHIP, MIPv6, MIPv4, DSMIPv6, DSMIPv4.

1. A method of establishing a traffic route for a mobile network nodeattached to a mobile router, wherein the mobile router has a pluralityof upstream interfaces available to it, the method comprising the stepsof: sending from the mobile router to the mobile node, identifiers ofthe interfaces and of their properties, the identifiers mapping to IPv6traffic classes or IPv4 type of service; at the mobile network node,choosing an interface based upon the identified interface properties;including in the traffic class or type of service field of at leastcertain outgoing packets the identifier of the chosen interface; and, atthe mobile router, causing packets to be routed across the interfacecorresponding to the identifier contained in the traffic class or typeof service fields.
 2. The method according to claim 1, wherein themobile router sends said identifiers within beacons broadcast by themobile router to advertise its presence.
 3. The method according toclaim 2, wherein said beacons are IPv6 router advertisement messages. 4.The method according to claim 3, wherein each identifier and associatedproperties are contained within an options field of the routeradvertisment messages.
 5. The method according to claim 4, wherein eachrouter advertisement message contains an options field for eachinterface.
 6. The method according to claim 1, wherein said step ofcausing packets to be routed across the interface corresponding to theidentifier contained in the packet headers comprises the steps of:receiving a packet at the mobile router from a downstream mobile networknode; identifying the traffic class or type of service field of thepacket header; establishing a rule at the mobile router for routingoutgoing packets across an interface corresponding to the traffic classor type of service; and, routing packets received from the mobilenetwork node according to said rule.
 7. The method according to claim 6,wherein said rule maps packet source and destination addresses to thechosen interface.
 8. The method according to claim 1, and furthercomprising the steps of sending a rule for routing incoming packets fromthe mobile router to a home agent of the mobile router and applying saidrule at the home agent.
 9. The method according to claim 8, wherein saidrule maps packet source and destination addresses to the choseninterface.
 10. The method according to claim 1, wherein the mobilenetwork node includes the identifier of the chosen interface in thetraffic class or type of service field of all packets belonging to agiven session.
 11. A mobile router, comprising: means for providing aplurality of upstream interfaces; a first transmitter for sending to amobile network node identifiers of the interfaces and of theirproperties, the identifiers mapping to IPv6 traffic classes or IPv4 typeof service; a receiver for receiving packets from downstream mobilenetwork nodes; means for mapping traffic class or type of service fieldswithin at least certain received packets to upstream interfaces; and, asecond transmitter for causing packets to be routed across theinterfaces corresponding to the identifiers contained in traffic classor type of service fields.
 12. The mobile router according to claim 11,wherein said first transmitter sends said identifiers within IPv6 routeradvertisement messages.
 13. The mobile router according to claim 12,wherein said first transmitter includes said identifiers in respectiveoptions fields of a router advertisement message.
 14. The mobile routeraccording to claim 10, further comprising means to establish a routingrule for a packet session, said rule mapping IP source and destinationaddresses to a chosen interface, and to route outgoing packets accordingto this rule.
 15. The mobile router according to claim 14, furthercomprising means to establish said rule when a first packet of thesession is received by the mobile router and to apply this rule tosubsequent packets of the session.
 16. The mobile router according toclaim 10, further comprising means for notifying a home agent of a rulefor causing an incoming packet session to be routed to the mobile routerover the same interface as used for the corresponding outgoing packetsession.